Various procedures employed in the petroleum industry involve the introduction of viscous liquids into wellbores. For example, in the production of oil from subterranean oil reservoirs by the waterflooding technique it is a common expedient to add polymeric thickening agents to all or part of the injected water in order to increase its viscosity for mobility and profile control purposes. Other techniques involve the injection of thickened aqueous solutions or gels into formations in order to selectively plug the formation adjacent production or injection wells and thus control the flow of fluids to and from such wells.
Many polymeric thickening agents have been proposed for use in such operations and in many cases the viscosity enhancing values of these polymers may be increased by the addition of trivalent metal ions which act as complexing or crosslinking agents. One well known group of polymers which may be employed either alone or in the presence of complexing agents is the polysaccharides produced by action of the genus Xanthomonas on carbohydrates. For example, U.S. Pat. No. 3,757,863 to Clampitt et al. discloses a process for effecting mobility control and/or plugging of a subterranean formation through the use of such polysaccharides in the presence of polyvalent metal ion crosslinking agents.
Crosslinked polysaccharides are also employed in other operations in which a thickened aqueous liquid is introduced into a wellbore. For example, U.S. Pat. No. 3,243,000 to Patton et al. discloses the use of trivalent ion complexed heteropolysaccharides produced by Xanthomonas bacteria as thickening agents in drilling fluids. Thus, a heteropolysaccharide produced by fermentation of sugar with the bacterium Xanthomonas campestris may be complexed by the addition of chromic chloride as a crosslinking agent. The polysaccharide and crosslinking agent may be added to water to effect the desired crosslinking and the resulting solution then mixed with oil under conditions to provide an oil-water emulsion drilling fluid. As recognized in the Patton et al. patent and also in U.S. Pat. No. 3,699,042 to Browning et al. and in Deily et al., "New Biopolymer Low-Solids Mud Speeds Drilling Operation", The Oil and Gas Journal, v. 65, No. 26, pp. 62-70 (June 26, 1967), such complexed polymer solutions exhibit higher viscosities than solutions of similar polymer concentrations without crosslinking.
Clampitt et al U.S. Pat. No. 3,908,760, describes such a proposed polymer flood process where a gelled water-soluble biopolysaccharide produced by the action of bacteria of the genus Xanthomonas on a carbohydrate is injected into a stratified reservoir to form a slug, band or front of gel extending vertically across both high permeability and low permeability strata. This band or front is then driven through the formation by a suitable drive fluid to produce oil adjacent to the flood front. This patent also suggests the use of complexed polysaccharides to block natural or man made fractures in formations.
In an attempt to selectively block high permeability strata of stratified formations, mechanical isolation of the thief zones has been tried. However, vertical communication among reservoir strata often renders such attempts ineffective.
Physical plugging of zones of high flow capacity by cements and solid slurries has also been attempted with varying degrees of success. Note L. R. Smith, C. R. Fast, and O. R. Wagner, "Development and Field Testing of Large Volume Remedial Treatments for Gross Water Channeling," J. Pet. Tech., 1015-1025, August, 1969; J. N. Breston, "Selective Plugging of Waterflood Input Wells, Theory, Methods, and Results," J. Pet. Tech., 26-31, March, 1957; T. M. Garland, "Selective Plugging of Water Injection Wells," J. Pet. Tech., 1550-1560, December 1966; J. O. Robertson, Jr., and F. H. Oefelein, "Plugging Thief Zones in Water Injection Wells," J. Pet. Tech., 999-1004, August, 1967; and W. F. Hower and J. Ramos, "Selective Plugging of Injection Wells by In Situ Reactions," J. Pet. Tech., 17-20, January, 1957. Here, the most serious drawback is the possibility of permanently closing the still oil productive horizons.
From these early experiences, the desirability of designing a viscous slug capable of sealing off the most permeable layers, of slowly moving from injector to producer, and of diverting the trailing floodwater to the underswept, tighter regions of the reservoir, became evident. This consideration led to the use of oil/water emulsions (note C. D. McAuliffe, "Oil-in-Water Emulsions Improve Fluid Flow in Porous Media," SPE 3784, Symposium on Improved Oil Recovery, Apr. 16-19, 1972, Tulsa), gels (note L. R. Smith, C. R. Fast, and O. R. Wagner, "Development and Field Testing of Large Volume Remedial Treatments for Gross Water Channeling," J. Pet. Tech., 1015-1025, August, 1969; J. O. Robertson, Jr., and F. H. Oefelein, "Plugging Thief Zones in Water Injection Wells," J. Pet. Tech., 999-1004, August, 1967; R. H. Knapp, M. E. Welbourn, "An Acrylic/Epoxy Emulsion Gel System for Formation Plugging: Laboratory Development and Field Testing for Steam Thief Zone Plugging," SPE 7083, Symposium on Improved Oil Recovery, Apr. 16-19, 1978, Tulsa; and B. J. Felber and D. L. Dauben, "Development of Lignosulfonate Gels for Sweep Improvement, SPE 6206, 51st Ann. Fall Tech. Conf. and Exh., Oct. 3-6, 1976, New Orleans), and polymers (note W. R. Townsend, S. A. Becker, and C. W. Smith, "Polymer Use in Calcareous Formation," SPE 6382, Symposium on Improved Oil Recovery, Apr. 16-19, 1978, Tulsa) with polymers being the most extensively applied during the past decade.
Among the polymers so far examined for improving waterflood conformance are polyacrylamides (note J. C. Mack, "Process Technology Improves Oil Recovery," SPE 7179, SPE Rocky Mountain Regional Meeting, May 17-19, 1978, Cody, Wyo.; W. G. Routson, M. Neale, and J. R. Penton, "A New Blocking Agent for Water Channeling," SPE 3992, 47th Ann. Fall Meeting of SPE-AIME, Oct. 8-11, 1972, San Antonio; D. Sparlin, "An Evaluation of Polyacrylamides for Reducing Water Production," J. Pet. Tech., 906-914, August, 1976; and G. P. Willhite and D. S. Jordan, "Alteration of Permeability in Porous Rocks with Gelled Polymers," 1981 ACS Meeting, Aug. 23-28, New York, Polymers Preprints), polysaccharides, carboxymethylcellulose (note R. W. Farley, J. F. Ellebracht, and R. H. Friedman, "Field Test of Self-Conforming Oil Recovery Fluid," SPE 5553, 50th Ann. Fall Meeting of SPE-AIME, Sept. 28-Oct. 1, 1975, Dallas) furfural-alcohol and acrylic/epoxy resins (note R. H. Knapp, M. E. Welbourn, "An Acrylic/Epoxy Emulsion Gel System for Formation Plugging: Laboratory Development and Field Testing for Steam Thief Zone Plugging," SPE 7083, Symposium on Improved Oil Recovery, Apr. 16-19, 1978, Tulsa; and P. H. Hess, C. O. Clark, C. A. Haskin and T. R. Hall, "Chemical Method for Formation Plugging," J. Pet. Tech., 559-564, May, 1971), WORCON.RTM. (note J. D. Weaver, "A New Water-Oil Ratio Improvement Material," SPE 7574, 53rd Ann. Fall Tech. Conf. & Exh., Oct. 1-3, 1978, Houston) and polyisocyanurate (note C. T. Presley, P. A. Argabright, R. E. Smith, and B. L. Phillips, "A New Approach to Permeability Reduction," SPE 4743, Symposium on Improved Oil Recovery, Apr. 22-24, 1974, Tulsa). An overwhelming fraction of the work has been conducted with the polyacrylamides.
Polyacrylamides have been used both in their normal, noncrosslinked form as well as in the form of metal complexes. In either state, the beneficial effects derived from these polyacrylamides seem to dissipate rapidly due to shear degradation during injection and sensitivity to reservoir brines. To overcome these problems and to achieve deeper penetration into the reservoir, dilute solutions of these polymers have sometimes been injected first and then complexed in situ. For example, in one such process, three sequential injection steps are employed: cationic polyacrylamides for strong adsorption and anchoring onto the generally anionic sites of the reservoir rock surfaces, chelation with aluminum ions provided by aluminum citrate or with chromium ions generated by the in situ reduction of Cr.sub.2 O.sub.7.sup..dbd. (note J. E. Hassert, and P. D. Flemming, III, "Gelled Polymer Technology for Control of Water in Injection and Production Wells," 3rd Conference on Tertiary Oil Recovery, U. of Kansas, Lawrence, 1979), and finally anionic polyacrylamides for the formation of the desired cationic polymer-metal ion-anionic polymer complexes. Recent field trails have shown these processes to have promise for enhanced oil recovery by injection profile control.
Like the polyacrylamides, polysaccharides may function as effective mobility improvement agents in waterflooding. They can also be complexed with multivalent cations in an attempt to provide highly viscous solutions, e.g., for stratification control and for floodwater diversion.